I think it's good for users if users mistake to write invalid mimetypes, WebKit finds plugin through file extensions.
Now, WebKit finds plugin through file extensions when a mimetype is only null.
How do you think about that?

Created attachment 206728[details]
Archive of layout-test-results from webkit-ews-06 for mac-mountainlion
The attached test failures were seen while running run-webkit-tests on the mac-ews.
Bot: webkit-ews-06 Port: mac-mountainlion Platform: Mac OS X 10.8.3

(In reply to comment #6)
> It’s generally not a good idea to disregard an explicitly provided MIME type.
I agree, but I don't feel too strongly about it.
However, if we don't have any evidence of real world web sites that are fixed by this change I don't think we should make it.